The present invention generally relates to ink delivery systems, and more particularly to a thermal inkjet printhead which is characterized by improved reliability, increased longevity, diminished production costs, cooler printhead operating temperatures, and greater overall printing efficiency. These goals are accomplished through the use of one or more novel resistor elements located within the printhead which are produced from a specialized alloy composition as discussed in considerable detail below.
Substantial developments have been made in the field of electronic printing technology. A wide variety of highly-efficient printing systems currently exist which are capable of dispensing ink in a rapid and accurate manner. Thermal inkjet systems are especially important in this regard. Printing units using thermal inkjet technology basically involve an apparatus which includes at least one ink reservoir chamber in fluid communication with a substrate (preferably made of silicon [Si] and/or other comparable materials) having a plurality of thin-film heating resistors thereon. The substrate and resistors are maintained within a structure that is conventionally characterized as a xe2x80x9cprintheadxe2x80x9d. Selective activation of the resistors causes thermal excitation of the ink materials stored inside the reservoir chamber and expulsion thereof from the printhead. Representative thermal inkjet systems are discussed in U.S. Pat. No. 4,500,895 to Buck et al.; U.S. Pat. No. 4,771,295 to Baker et al.; U.S. Pat. No. 5,278,584 to Keefe et al.; and the Hewlett-Packard Journal, Vol. 39, No. 4 (August 1988), all of which are incorporated herein by reference.
The ink delivery systems described above (and comparable printing units using thermal inkjet technology) typically include an ink containment unit (e.g. a housing, vessel, or tank) having a self-contained supply of ink therein in order to form an ink cartridge. In a standard ink cartridge, the ink containment unit is directly attached to the remaining components of the cartridge to produce an integral and unitary structure wherein the ink supply is considered to be xe2x80x9con-boardxe2x80x9d as shown in, for example, U.S. Pat. No. 4,771,295 to Baker et al. However, in other cases, the ink containment unit will be provided at a remote location within the printer, with the ink containment unit being operatively connected to and in fluid communication with the printhead using one or more ink transfer conduits. These particular systems are conventionally known as xe2x80x9coff-axisxe2x80x9d printing units. Representative, non-limiting off-axis ink delivery systems are discussed in co-owned U.S. Pat. No. 6,158,853 to Olsen et al. and co-owned U.S. Pat. No. 5,975,686 to Hauck et al. which are each incorporated herein by reference. The present invention is applicable to both on-board and off-axis systems (as well as any other types which include at least one ink containment vessel that is either directly or remotely in fluid communication with a printhead containing at least one ink-ejecting resistor therein as will become readily apparent from the discussion provided below.)
Regardless of the particular ink delivery system being employed, an important factor to consider involves the operating efficiency of the printhead with particular reference to the resistor elements that are used to expel ink on-demand during printhead operation. The term xe2x80x9coperating efficiencyxe2x80x9d shall encompass a number of different items including but not limited to internal temperature levels, ink delivery speed, expulsion frequency, energy requirements (e.g. current consumption), and the like. Typical and conventional resistor elements used for ink ejection in a thermal inkjet printhead are produced from a number of compositions including but not limited to a mixture of elemental tantalum [Ta] and elemental aluminum [Al] (also known as xe2x80x9cTaAlxe2x80x9d), as well as other comparable materials including tantalum nitride (xe2x80x9cTa2Nxe2x80x9d). Standard ink delivery resistor systems are discussed in considerable detail in U.S. Pat. No. 4,535,343 to Wright et al.; U.S. Pat. No. 4,616,408 to Lloyd; and U.S. Pat. No. 5,122,812 to Hess et al. which are all incorporated herein by reference.
However, the chemical and physical characteristics of the resistor elements which are selected for use in a thermal inkjet printhead will directly influence the overall operating efficiency of the printhead. It is especially important that the resistor elements (and resistive materials associated therewith) be as energy efficient as possible and are capable of operating at low current levels. Resistive compounds having high current requirements are typically characterized by numerous disadvantages including a need for high cost, high-current power supplies in the printer unit under consideration. Likewise, additional losses of electrical efficiency can occur which are caused by the passage of greater current levels through the electrical xe2x80x9cinterconnect structuresxe2x80x9d (circuit traces, etc.) in the printhead that are attached to the resistor(s), with such interconnect structures exhibiting xe2x80x9cparasitic resistancesxe2x80x9d. These parasitic resistances cause increased energy losses as greater current levels pass therethrough, with such energy losses being reduced when current levels are diminished. Likewise, high current requirements in the resistor elements and the xe2x80x9cparasitic resistancesxe2x80x9d mentioned above can result in (1) greater overall temperatures within the printhead (with particular reference to the substrate or xe2x80x9cdiexe2x80x9d on which the printhead components are positioned [discussed further below]); and (2) lower printhead reliability/longevity levels.
While conventional resistor materials including TaAl and Ta2N have functioned adequately in thermal inkjet printing systems of the types discussed above, the foregoing disadvantages are nonetheless an important consideration which leaves room for improvement. In this regard, a need remained (prior to development of the present invention) for a resistor system suitable for use in thermal inkjet printing systems of all types which is capable of high efficiency/low current operation. The present invention satisfies this need by providing novel resistor elements that represent a substantial improvement over prior resistor units. The resistor elements of the claimed invention specifically offer a number of advantages including but not limited to: (1) decreased current requirements which lead to improved electrical efficiency; (2) reductions in printhead operating temperatures with particular reference to the substrate or xe2x80x9cdiexe2x80x9d; (3) the general promotion of more favorable temperature conditions within the printhead (which result from reduced current requirements that correspondingly decrease current-based parasitic heat losses from xe2x80x9cinterconnect structuresxe2x80x9d attached to the resistors); (4) multiple economic benefits including the ability to use less-costly, high voltage/low current power supplies; (5) improved overall reliability, stability, and longevity levels in connection with the printhead and resistor elements; (6) the avoidance of heating efficiency problems which can lead to resistor xe2x80x9chot spotsxe2x80x9d, absolute limits on resistance, and the like; (7) greater xe2x80x9cbulk resistivityxe2x80x9d as defined below compared with conventional resistor materials such as TaAl and Ta2N; (8) the ability to place more resistors within a given printhead in view of the reduced operating temperatures listed above; (9) a reduction in electromigration problems; and (10) generally superior long-term operating performance. As will become readily apparent from the discussion provided below, the novel materials selected for use in producing the claimed resistor elements offer these and other important benefits. The structures discussed herein therefore constitute a substantial advance in the art of thermal inkjet printhead design compared with prior (e.g. conventional) systems.
In accordance with the detailed information provided below, the present invention involves a thermal inkjet printhead having one or more novel resistor elements therein which are unique in structure, construction materials, and functional capability. Also encompassed within the invention is an ink delivery system using the claimed printhead and a manufacturing method for producing the printhead. Each of these developments will be outlined in considerable detail below. Accordingly, the present invention again represents a significant advance in thermal inkjet technology which ensures high levels of operating efficiency, excellent image quality, rapid throughput, and increased longevity which are important goals in any printing system.
It is an object of the present invention to provide a highly efficient thermal inkjet printhead which is characterized by improved operating efficiency.
It is another object of the invention to provide a highly efficient thermal inkjet printhead which employs an internal structure that offers superior thermal stability.
It is another object of the invention to provide a highly efficient thermal inkjet printhead which employs at least one or more heating resistors therein that are characterized by improved electrical efficiency resulting from reduced current requirements.
It is another object of the invention to provide a highly efficient thermal inkjet printhead which employs at least one or more heating resistors that are characterized by reductions in printhead operating temperatures with particular reference to the substrate or xe2x80x9cdiexe2x80x9d on which the resistors and interconnect structures are positioned.
It is another object of the invention to provide a highly efficient thermal inkjet printhead which employs at least one or more heating resistors that promote favorable temperature conditions within the printhead as previously discussed which result in higher-speed printing, better image quality, and the like.
It is another object of the invention to provide a highly efficient thermal inkjet printhead which employs increased numbers of heating resistors per unit area compared with conventional systems.
It is a further object of the invention to provide a highly efficient thermal inkjet printhead which employs at least one or more heating resistors that are likewise characterized by a number of economic benefits including but not limited to the ability to use less-costly, high voltage/low current power supplies in the printing system under consideration.
It is a further object of the invention to provide a highly efficient thermal inkjet printhead which employs at least one or more heating resistors that are also characterized by the avoidance of heating efficiency problems which can lead to resistor xe2x80x9chot spotsxe2x80x9d, absolute limits on resistance, and the like.
It is a further object of the invention to provide a highly efficient thermal inkjet printhead which employs at least one or more heating resistors that are also characterized by their ability to provide all of the foregoing benefits while being configured in a number of different shapes, sizes, and orientations without limitation.
It is a further object of the invention to provide a highly efficient thermal inkjet printhead which accomplishes the goals listed above while avoiding any requirement that additional material layers and components be used in the printhead.
It is a further object of the invention to provide a highly efficient thermal inkjet printhead in which the beneficial features thereof yield a printing system that is characterized by rapid operation and the generation of stable printed images.
It is a further object of the invention to provide a highly efficient thermal inkjet printhead in which the claimed structures are readily manufactured in an economical fashion on a mass-production scale.
It is a further object of the invention to provide a rapid and effective method for manufacturing a thermal inkjet printhead having the beneficial characteristics, features, and advantages outlined herein.
It is a further object of the invention to provide a rapid and effective method for manufacturing a thermal inkjet printhead having the beneficial characteristics, features, and advantages outlined herein which uses a minimal number of process steps.
It is an even further object of the invention to provide a specialized printhead of the type described above which is readily applicable to a wide variety of different ink delivery systems including (1) on-board cartridge-type units having a self-contained supply of ink associated therewith; and (2) off-axis systems as previously discussed in which the claimed printhead is operatively connected to a remotely-positioned ink containment vessel using one or more tubular conduits.
A novel and highly efficient thermal inkjet printhead is described below which provides numerous advantages over prior systems. As previously stated, the claimed printhead employs at least one resistor element (or, more simply, a xe2x80x9cresistorxe2x80x9d) which is characterized by a number of benefits compared with conventional systems. These benefits again include increased electrical efficiency (e.g. reduced current consumption), the promotion of more favorable temperature conditions within the printhead structure including reduced substrate or xe2x80x9cdiexe2x80x9d temperatures, and greater overall levels of reliability, longevity, and stability. These and other benefits associated with the claimed invention will become readily apparent from the discussion provided below in the Detailed Description of Preferred Embodiments section.
As a preliminary point of information, the present invention shall not be restricted to any particular types, sizes, or arrangements of internal printhead components unless otherwise stated herein. Likewise, the numerical parameters listed in this section and the other sections below constitute preferred embodiments designed to provide optimum results and shall not limit the invention in any respect. All recitations of chemical formulae and structures provided herein are designed to generally indicate the types of materials which may be used in the claimed invention. The listing of specific chemical compositions which fall within the general formulae presented below are provided for example purposes only and shall be considered non-limiting.
The claimed invention and its novel developments are applicable to all types of thermal inkjet printing systems provided that they include (1) at least one support structure as discussed in the Detailed Description of Preferred Embodiments section; and (2) at least one ink-ejecting resistor element located inside the printhead which, when energized, will provide sufficient heat to cause ink materials in proximity therewith to be thermally expelled from the printhead. The claimed invention shall therefore not be considered printhead or support structure-specific and is not limited to any particular applications, uses, and ink compositions. Likewise, the terms xe2x80x9cresistor elementxe2x80x9d and/or xe2x80x9cresistorxe2x80x9d shall be construed to cover one resistor or groups of multiple resistors regardless of shape, material-content, or dimensional characteristics.
It is a primary goal to provide improved stability, economy, reliability, and longevity in the printhead structures of this invention. For the sake of clarity and in order to adequately explain the invention, specific materials and processes will again be recited in the Detailed Description of Preferred Embodiments section with the understanding that these items are being described for example purposes only in a non-limiting fashion.
It should also be understood that the claimed invention shall not be restricted to any particular construction techniques (including any given material deposition procedures) unless otherwise stated below. For example, the terms xe2x80x9cformingxe2x80x9d, xe2x80x9capplyingxe2x80x9d, xe2x80x9cdeliveringxe2x80x9d, xe2x80x9cplacingxe2x80x9d, and the like as used throughout this discussion to describe the assembly of the claimed printhead shall broadly encompass any appropriate manufacturing procedures. These processes range from thin-film fabrication techniques and sputter deposition methods to pre-manufacturing the components in question (including the resistor elements) and then adhering these items to the designated support structures using one or more adhesive compounds which are known in the art for this purpose. In this regard, the invention shall not be considered xe2x80x9cproduction method specificxe2x80x9d unless otherwise stated herein.
As previously noted, a highly effective and durable printhead containing one or more novel resistor elements is provided for use in an ink delivery system. The term xe2x80x9cink delivery systemxe2x80x9d shall, without limitation, involve a wide variety of different devices including cartridge units of the xe2x80x9cself-containedxe2x80x9d type having a supply of ink stored therein. Also encompassed within this term are printing units of the xe2x80x9coff-axisxe2x80x9d variety which employ a printhead connected by one or more conduit members to a remotely-positioned ink containment unit in the form of a tank, vessel, housing, or other equivalent structure. Regardless of which ink delivery system is employed in connection with the claimed printhead, the present invention is capable of providing the benefits listed above which include more efficient and rapid operation.
The following discussion shall constitute a brief and general overview of the invention. More specific details concerning particular embodiments, best modes, and other important features of the invention will again be recited in the Detailed Description of Preferred Embodiments section set forth below. All scientific terms used throughout this discussion shall be construed in accordance with the traditional meanings attributed thereto by individuals skilled in the art to which this invention pertains unless a special definition is provided herein.
The claimed invention involves a novel resistor-containing inkjet printhead which is characterized by improved functional characteristics, namely, more efficient operation with reduced current consumption and the promotion of favorable temperature conditions within the printhead. As a result, a greater degree of cool-down can occur between ink-ejection cycles, along with reduced peak operating temperatures, decreased energy requirements, the ability to use greater numbers of resistors per unit area, and the like. The components and novel features of this system will now be discussed. In order to produce the claimed printhead, a support structure is initially provided on which the resistor elements of the invention reside. The support structure typically comprises a substrate which is optimally manufactured from elemental silicon [Si], although the present invention shall not be exclusively restricted to this material with a number of other alternatives being outlined below. The support structure may have at least one or more layers of material thereon including but not limited to an electrically-insulating base layer produced from, for example, silicon dioxide [SiO2]. The term xe2x80x9csupport structurexe2x80x9d as used herein shall therefore encompass (1) the substrate by itself if no base layer or other materials are positioned thereon; and (2) the substrate and any other material layers thereon which form a composite structure on which the resistors reside or are otherwise positioned. In this regard, the phrase xe2x80x9csupport structurexe2x80x9d shall generally involve the layer or layers of material (whatever they may be) on which the resistor elements are placed/formed.
Also provided as part of the printhead in a preferred and non-limiting embodiment is at least one layer of material which specifically comprises at least one opening or xe2x80x9corificexe2x80x9d therethrough. This orifice-containing layer of material may be characterized as an xe2x80x9corifice platexe2x80x9d, xe2x80x9corifice structurexe2x80x9d, xe2x80x9ctop layerxe2x80x9d, and the like. Furthermore, single or multiple layers of materials may be employed for this purpose without restriction, with the terms xe2x80x9corifice platexe2x80x9d, xe2x80x9corifice structurexe2x80x9d, etc. being defined to encompass both single and multiple layer embodiments. The resistor element(s) of the present invention are positioned between the orifice-containing layer of material and the support structure as discussed below. Again, additional detailed information regarding these components, what they are made from, how they are arranged, and the manner in which they are assembled/fabricated will be outlined below in the Detailed Description of Preferred Embodiments section.
With continued reference to the printhead components mentioned above, at least one resistor element is positioned within the printhead between the support structure and the orifice-containing layer for expelling ink on-demand from the printhead. The resistor is in fluid communication with a supply of ink as shown in the accompanying drawing figures so that effective printing can occur. Likewise, the resistor is specifically placed on the support structure in a preferred embodiment, with the terms xe2x80x9cplacedxe2x80x9d, xe2x80x9cpositionedxe2x80x9d, xe2x80x9clocatedxe2x80x9d, xe2x80x9corientedxe2x80x9d, xe2x80x9coperatively attachedxe2x80x9d, xe2x80x9cformedxe2x80x9d, and the like relative to placement of the resistor on the support structure encompassing a situation in which (1) the resistor is secured directly on and to the upper surface of the substrate without any intervening material layers therebetween; or (2) the resistor is xe2x80x9csupportedxe2x80x9d by the substrate in which one or more intermediate material layers (including the insulating base layer) are nonetheless located between the substrate and resistor. Both of these alternatives shall be considered equivalent and encompassed within the present claims.
In accordance with the novel character of the claimed invention, the resistor element (also characterized herein as simply a xe2x80x9cresistorxe2x80x9d as previously noted) is produced from at least one composition which shall be designated herein as a xe2x80x9cmetal silicon nitridexe2x80x9d compound. Such a material basically involves an alloy of at least one or more metals [M], silicon [Si], and nitrogen [N] in order to form a nitride composition having the desired characteristics. From a general standpoint, the metal silicon nitrides of the claimed invention will have the following formula: xe2x80x9cMSiNxe2x80x9d and, more specifically, xe2x80x9cMxSiyNzxe2x80x9d wherein xe2x80x9cMxe2x80x9d=at least one metal as noted above, xe2x80x9cXxe2x80x9d=about 12-38 (optimum=about 18-25), xe2x80x9cSixe2x80x9d=silicon, xe2x80x9cYxe2x80x9d=about 27-45 (optimum=about 32-35), xe2x80x9cNxe2x80x9d=nitrogen, and xe2x80x9cZxe2x80x9d=about 20-60 (optimum=about 35-47), with the foregoing numbers being non-restrictive and provided herein for example purposes only. Likewise, the numbers and ranges listed above can be employed in various combinations without limitation in accordance with the invention. It shall therefore be understood that the present invention, in its most general form, will encompass a resistor structure comprising, in combination, at least one metal combined with silicon and nitrogen that is located between the support structure and the orifice-containing layer in a printhead. Specific materials, proportions, fabrication techniques, and the like which are identified herein shall be considered representative and non-limiting unless otherwise stated.
Many different metals [M] may be included within the formula listed above without restriction. However, in a preferred embodiment designed to provide optimum results, the transition metals (e.g. metals in groups IIIB to IIB of the periodic table) are best, with optimum materials in this group including but not limited to elemental tantalum [Ta], tungsten [W], chromium [Cr], molybdenum [Mo], titanium [Ti], zirconium [Zr], hafnium [Hf], and mixtures thereof. Also, other metals [M] which are prospectively applicable in the formula listed above include non-transition metals (e.g. aluminum [Al]) as selected by routine preliminary testing although at least one or more transition metals are again preferred. While many specific formulations can be produced which will fall within the general chemical structures recited herein, a number of particular metal silicon nitrides that provide optimum results include but are not limited to: W30Si36N32, W36Si39N24, W17Si38N45, W17Si40N43, W19Si34N47, W17Si36N47, W21Si30N49, W28Si32N40, W23Si30N47, W24Si39N37, W26Si30N44, W27Si36N35, W36Si27N36, W13Si37N50, W25Si32N43, W18Si35N47, Ta21Si34N45, Ta20Si36N44, Ta18Si35N47, Ta25Si32N43, Ta13Si37N50, Ta36Si27N36, Cr20Si39N41, Cr21Si41N37, Cr18Si35N47, Cr13Si37N50, Cr25Si32N43, Cr37Si27N36, Mo22Si38N40, Mo12Si38N50, Mo18Si35N47, Mo25Si32N43, Mo36Si27N37, and mixtures thereof. Again, these materials are listed as examples only and shall not limit the invention in any respect.
The metal silicon nitride resistors described herein create a novel and effective ink-ejection system for use in a thermal inkjet printhead. As previously stated, they are characterized by many significant benefits. One factor of importance is their relatively high bulk resistivity compared within conventional materials including resistors made from tantalum-aluminum [TaAl] and tantalum nitride [Ta2N] mixtures/alloys. While this aspect of the present invention will be outlined in greater detail below, the term xe2x80x9cbulk resistivityxe2x80x9d (or, more simply, xe2x80x9cresistivityxe2x80x9d) shall be conventionally defined herein to involve a xe2x80x9cproportionality factor characteristic of different substances equal to the resistance that a centimeter cube of the substance offers to the passage of electricity, the current being perpendicular to two parallel facesxe2x80x9d as noted in the CRC Handbook of Chemistry and Physics, 55th ed., Chemical Rubber Publishing Company/CRC Press, Cleveland Ohio, (1974-1975), p. F-108. In general, bulk resistivity (or resistivity as previously stated) shall be determined in accordance with the following formula:
xcfx81=Rxc2x7(A/L)
wherein:
R=the resistance of the material in question
A=the cross-sectional area of the resistor; and
L=the length of the resistor
Bulk resistivity/resistivity values are typically expressed in microohm-centimeters or xe2x80x9cxcexcxcexa9-cmxe2x80x9d. High bulk resistivity values are desirable in the resistor structures employed in thermal inkjet printing units for various reasons including the ability of structures having these characteristics to provide greater levels of electrical and thermal efficiency compared with conventional resistive compounds as previously discussed. In accordance with the general parameters, formulae, and other information presented above, the claimed metal silicon nitride materials associated with the present invention will have a preferred and representative bulk resistivity value of about 1400-30,000 xcexcxcexa9-cm (optimum=about 3000-10,000 xcexcxcexa9-cm), although the claimed invention shall not be restricted to these values. For comparison purposes, traditional resistive materials and resistors of comparable size, shape, and configuration made from, for example, TaAl and/or Ta2N have typical bulk resistivity values of about 200-250 xcexcxcexa9cm which are considerably less than those recited above in connection with the claimed metal silicon nitrides. In this regard, the benefits of the present invention are readily apparent and self-evident.
While additional information concerning the orientation of the claimed resistor elements in the printhead, thickness values thereof, and other relevant parameters shall be recited below in the Detailed Description of Preferred Embodiments section, various factors of particular relevance merit further discussion at this time. For example, each of the resistors which are produced from at least one or more metal silicon nitride materials will have an exemplary and preferred (non-limiting) thickness of about 300-4000 xc3x85. However, the ultimate thickness of any given resistor shall be determined and may be varied in accordance with routine preliminary pilot testing involving a number of factors including the type of printhead under consideration and the particular construction materials being employed. As discussed below and illustrated in the accompanying drawing figures, each of the claimed resistors will optimally be in at least partial or (preferred) complete axial alignment (e.g. xe2x80x9cregistryxe2x80x9d) with at least one of the openings in the orifice-containing layer of material so that rapid, accurate, and effective inkjet printing can occur.
The Detailed Description of Preferred Embodiments section will provide further and more specific data involving the fabrication techniques which may be used to apply or otherwise form the resistor elements on the support structure within the printhead. The invention shall not be restricted to any particular fabrication techniques with a number of approaches being applicable as outlined below. Of particular interest is the use of one or more sputtering processes which will be reviewed extensively in the next section.
In accordance with the present invention, an xe2x80x9cink delivery systemxe2x80x9d is likewise provided in which an ink containment vessel is operatively connected to and in fluid communication with the printhead described above which contains the metal silicon nitride resistors. As specifically discussed below, the term xe2x80x9coperatively connectedxe2x80x9d relative to the printhead and ink containment vessel shall involve a number of different situations including but not limited to (1) cartridge units of the xe2x80x9cself-containedxe2x80x9d type in which the ink containment vessel is directly attached to the printhead to produce a system having an xe2x80x9con-boardxe2x80x9d ink supply; and (2) printing units of the xe2x80x9coff-axisxe2x80x9d variety which employ a printhead connected by one or more conduit members (or similar structures) to a remotely-positioned ink containment unit in the form of a tank, vessel, housing, or other equivalent structure. The novel printhead structures of the present invention shall not be limited to use with any particular ink containment vessels, the proximity of these vessels to the printheads, and the means by which the vessels and printheads are attached to each other.
Finally, the present invention shall also encompass a method for producing the claimed printhead structures which incorporate the novel metal silicon nitride resistors. The fabrication steps that are generally used for this purpose involve the materials and components listed above, with the previously-described summary of these items being incorporated by reference in this discussion. The basic production steps are as follows: (1) providing a support structure (defined above); (2) forming at least one resistor element thereon, with the resistor element being comprised of one or more metal silicon nitride compositions (previously discussed); (3) providing at least one layer of material which comprises at least one opening therethrough (see the explanation and definition set forth above in connection with this structure); and (4) securing the layer of material comprising the opening therein in position above the substrate and resistor element in order to produce the printhead. The terms xe2x80x9cformingxe2x80x9d, xe2x80x9cfabricatingxe2x80x9d, xe2x80x9cproducingxe2x80x9d, and the like relative to placement of the resistor element on the substrate will involve the following situations which shall be deemed equivalent: (A) creating a resistor structure using one or more metal-layer fabrication stages on the support structure as previously defined (with sputtering being preferred); or (B) pre-manufacturing the resistor element in question and thereafter securing it on the support structure using chemical or physical attachment means (soldering, adhesive affixation, and the like).
The resistor element may also be xe2x80x9cstabilizedxe2x80x9d to prevent undesired fluctuations in resistance during subsequent use. Many different stabilization procedures can be used without limitation. However, in a preferred embodiment, resistor stabilization can be achieved by: (1) heating the metal silicon nitride resistor element(s) to a temperature of about 800-1000xc2x0 C. for a non-limiting time period of about 10 seconds to several minutes; or (2) applying about 1xc3x97102 to 1xc3x97107 pulses of electrical energy to the resistor element(s), with each pulse having about 20-500% greater energy than the xe2x80x9cturn-on energyxe2x80x9d of the resistor element under consideration (with the applicable voltage and current parameters being readily determined from the resistance value of the resistor and the energy recited above), a pulse-width of about 0.6-100 xcexcsec. (microseconds), a pulse voltage of about 10-160 volts, a pulse current of about 0.03-0.2 amps, and a pulse frequency of about 5-100 kHz. In a non-limiting and representative (e.g. preferred) example, for a 30 xcexcmxc3x9730 xcexcm 300xcexa9 metal silicon nitride resistor with a turn-on energy of 2.0 xcexcJ, a typical stabilizing pulse treatment process would involve the following parameters: an energy level which is 80% above the foregoing turn-on value, 46.5 volts, 0.077 amps, 1 xcexcsec. pulse-width, 50 kHz pulse frequency, and 1xc3x97103 pulses. However, these numbers are again provided for example purposes only and may be varied within the scope of the invention through routine preliminary pilot testing.
The completed printhead is designed to generate a printed image from an ink supply (which is in fluid communication with the printhead/resistors) in response to a plurality of successive electrical impulses delivered to the resistor(s). In accordance with the novel features of the invention outlined herein, the use of a selected metal silicon nitride compound will reduce overall current requirements in the printing system, thereby creating many benefits including power supply cost reductions and more favorable thermal profiles within the printhead. The specific chemical compositions, numerical parameters, preferred bulk resistivity values (about 1400-30,000 xcexcxcexa9-cm), and other previously-described data associated with the metal silicon nitride materials are entirely applicable to the claimed method. Likewise, the step of forming the desired resistor element(s) on the support structure will involve fabricating resistors thereon having a preferred, non-limiting thickness of about 300-4000 xc3x85 (which is again subject to variation as needed in accordance with routine preliminary testing.)
Finally, the fabrication process is completed by attaching (e.g. applying, delivering, etc.) at least one layer of material having at least one orifice (e.g. opening) therethrough in position over and above the substrate and resistor so that the orifice is in partial or (preferably) complete axial alignment (e.g. xe2x80x9cregistryxe2x80x9d) with the resistor and vice versa. The orifice again allows ink materials to pass therethrough and out of the printhead during ink delivery. As a result of this process, the completed printhead will include (1) a support structure; (2) at least one layer of material positioned above the support structure and spaced apart therefrom which has at least one opening therethrough; and (3) at least one resistor element positioned within the printhead between the support structure and the orifice-containing layer for expelling ink on-demand from the printhead, wherein the resistor element is comprised of at least one metal silicon nitride composition as previously defined. The many benefits provided by this invention as discussed above are directly attributable to the use of a metal silicon nitride resistor system in the claimed printhead.
The present invention represents a significant advance in the art of thermal inkjet technology and the generation of high-quality images with improved reliability, speed, longevity, stability, and electrical/thermal efficiency. The novel structures, components, and methods described herein offer many important benefits including but not limited to: (1) decreased current requirements which lead to improved electrical efficiency; (2) reductions in printhead operating temperatures with particular reference to the substrate or xe2x80x9cdiexe2x80x9d; (3) the general promotion of more favorable temperature conditions within the printhead (which result from reduced current requirements that correspondingly decrease current-based parasitic heat losses from xe2x80x9cinterconnect structuresxe2x80x9d attached to the resistors); (4) multiple economic benefits including the ability to use less-costly, high voltage/low current power supplies; (5) improved overall reliability, stability, and longevity levels in connection with the printhead and resistor elements; (6) the avoidance of heating efficiency problems which can lead to resistor xe2x80x9chot spotsxe2x80x9d, absolute limits on resistance, and the like; (7) greater xe2x80x9cbulk resistivityxe2x80x9d as defined below compared with conventional resistor materials such as TaAl and Ta2N; and (8) the ability to place more resistors within a given printhead in view of the reduced operating temperatures listed above; (9) a reduction in electromigration problems; and (10) generally superior long-term operating performance. These and other benefits, objects, features, and advantages of the invention will become readily apparent from the following Brief Description of the Drawings and Detailed Description of Preferred Embodiments.